Experimental investigation of ship airwake with wave-induced motions

The turbulent airwake over a moving ship is experimentally investigated in a wind-wave facility using a 1:200 scaled NATO-GD model. Three motion scenarios are examined: heaving, pitching, and combined motions, naturally driven by incoming waves. Particle Image Velocimetry measurements are conducted along the ship centreline and at a typical helicopter rotor hover height. A phase-resolved analysis is performed to isolate the effects of ship displacement, orientation, and moving direction on the airwake. The results show that the ship motion directly contributes to the airwake vertical velocity with a phase delay, while the streamwise velocity is primarily governed by ship geometry. Compared with pure heaving, pitching motion induces stronger phase-dependent turbulence variations over the landing deck due to interactions between upstream structure wakes. Elevated turbulence levels are generally associated with positive heave displacements and negative pitch angles. In addition, the hangar geometry introduces large velocity gradients and alters turbulence distribution across the deck. A probabilistic approach is adopted to quantitatively assess the motion impact on helicopter landing safety. The results demonstrate significant dependence of landing risk on motion type, motion phase, and hover height. Generally, the combined motion and a higher hover height lead to less favourable flying conditions.